1. Field of the Invention
The present invention relates to an improved well tubular hanger having a seal system suitable for operation when subjected to wide variations in temperature. Such temperature variations may be experienced, for example, during production in Alaska (-75.degree. F. to 250.degree. F.) and in steam injection applications (up to 1000.degree. F.).
2. Description of the Prior Art
As discussed in U.S. Pat. No. 4,190,270 issued Feb. 26, 1980 to Vanderford, entitled "Tubing Hanger for Temperature Variations and Extremes", a tubing system is disclosed wherein the pressure seal is maintained by a metal seal ring. As shown in FIG. 3 of this patent, a sleeve is used to force the metal seal ring downwardly within an annular space defined between the head and body of the apparatus. The location of the seal ring provides an additional pressure boundary between pressurized annulus fluids and wellhead components located above the seal ring. Operation of the seal ring, however, requires actuation of a pin 128 to force sleeve 124 downward. The opening required for pin 128 through the head 100 creates a potential leak spot through the head.
A seal apparatus therefore needs to be developed that minimizes the amount of potential leak sources from the head of a well. Such a system should provide a positive pressure seal when it is desired to isolate a potentially pressurized annulus from wellhead components located above the tubing hanger.